In some cases it makes sense to block a phone number from calling. Once the call is blocked the phone system will no longer process calls from that person. The person will get a busy signal if they call again after being blocked.
To block the last caller let the incoming call finish ringing. Dial *32 on your softphone or handset.
The phone system will repeat the number back to you. If the number is correct press 1.
The block happens immediately.